In the field of mobile communications, it is well know to provide for the relocation of the network access point of an established call to a user equipment as the user equipment roams in the network.
A TPC (transmission power control) CI (combination index) is an integer value in the range 0 to 5. Each time a radio link is established, a TPC CI is allocated for the link. A radio link is a connection from a radio network controller (RNC) to a user equipment (UE) via a base station. All radio links established via a given base station (Node B) must have the same TPC CI. If a new radio link is established using a Node B which has no previous radio links, then a new non-used TPC CI must be allocated for that Node B.
The UE uses the TPC CI to control the power for different radio links. Radio links from the same Node B are handled as a group from a power control point of view.
Whilst all radio links established via a given Node B have the same TPC CI, the various radio links established through the Node B are uniquely identified by a Primary common pilot channel (CPICH) info.
The TPC CI is established between the radio network controller (RNC) and the user equipment (UE), and it is not known by the base stations. The TPC CI is always allocated by the RNC that establishes a radio link.
When RNC relocation occurs, the new RNC does not know the TPC CI(s) of the radio links that were established by the original RNC, despite the fact that these radio links are transferred to the new RNC.
The TPC CI has a very limited value range, being an integer value in the range 0 to 5. Thus, when a new RNC starts to establish a new radio link to a new base station/user equipment after relocation it may accidentally allocate a TPC CI that is already in use. This creates a situation where the UE has the incorrect power control information. If the new RNC allocates a TPC CI that is already in use by another RNC, then the UE will assume that the new radio link is under the control of the same base station as the old radio link(s).
It is an aim of the present invention to provide an improved technique for serving radio network subsystem relocation.